What Does a Dry Sauna Actually Do? The 20-Year Data

Over 20 years, sudden cardiac death hit 5.0% of frequent sauna users vs 10.1% of weekly users. What the Finnish data shows, and its limits.

By Hydra Editorial

In a Finnish cohort of 2,315 middle-aged men followed for a median of 20.7 years, sudden cardiac death occurred in 10.1% of men who used a sauna once a week and 5.0% of those using it 4 to 7 times a week. All-cause mortality was 49.1% versus 30.8%. The dose-response pattern is what makes the sauna literature unusual: more sessions, and longer ones, tracked with lower risk.

What did the Finnish sauna study actually find?

The Kuopio Ischaemic Heart Disease study, published in JAMA Internal Medicine in 2015, recorded 190 sudden cardiac deaths, 407 fatal cardiovascular events and 929 deaths overall. After adjustment for cardiovascular risk factors, men using a sauna 4 to 7 times per week had a hazard ratio of 0.37 for sudden cardiac death (95% CI 0.18 to 0.75) compared with once-weekly users, and 0.50 for fatal cardiovascular disease. Session length mattered too: sessions over 19 minutes carried a hazard ratio of 0.48 for sudden cardiac death versus sessions under 11 minutes.

The same cohort produced a 2017 analysis in Age and Ageing on cognitive outcomes. Dementia was diagnosed in 10% of once-weekly users and 4% of the 4-to-7-times group, giving an adjusted hazard ratio of 0.34 (95% CI 0.16 to 0.71).

How much of this can be trusted?

This is observational work in a population where sauna use is near-universal, which cuts both ways. It gives the study a genuine range of exposure that almost no other country could supply. It also means the highest-frequency group was small: only 201 of 2,315 men, which is why the confidence intervals are wide.

The obvious alternative explanation is reverse causation. Men healthy enough to sit in a hot sauna room four times a week may simply have been healthier to begin with. The researchers adjusted for physical activity, cardiorespiratory fitness, smoking, blood pressure, cholesterol and diabetes, and the associations held. That strengthens the case without settling it. No randomized trial has tested sauna frequency against hard cardiovascular endpoints, and until one does, the honest description is a strong, consistent, dose-dependent association.

A proposed mechanism, drawn from the broader sauna physiology literature rather than this cohort specifically, is that sustained heat raises heart rate into a moderate-exercise range, drops peripheral vascular resistance, and improves measures of arterial stiffness and endothelial function acutely. Tracking your own cardiovascular markers over time is the only way to know whether that applies to you.

The bottom line

  • Sudden cardiac death occurred in 5.0% of frequent sauna users versus 10.1% of once-weekly users over roughly 21 years of follow-up
  • Sessions longer than 19 minutes were associated with roughly half the sudden cardiac death risk of sessions under 11 minutes
  • The frequent-use group was only 201 men, and no randomized trial has tested this, so treat the effect size as indicative rather than settled

Frequently asked questions

How often do you need to use a sauna to see the associations in the research?
The Finnish cohort found the largest differences at 4 to 7 sessions per week compared with 1 session per week, with an intermediate effect at 2 to 3 sessions. Risk decreased continuously with frequency in a later analysis of the same cohort, with no threshold below which the association disappeared.
Is dry sauna as good as exercise?
No study has established that. The Finnish analyses adjusted for cardiorespiratory fitness and physical activity, meaning the sauna association was measured on top of exercise, not in place of it. A separate analysis of the same cohort found the lowest risk in men who had both high fitness and frequent sauna use.

Sources

  1. Laukkanen T et al., 2015. Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events. JAMA Internal Medicine 175(4):542-548.
  2. Laukkanen T et al., 2017. Sauna bathing is inversely associated with dementia and Alzheimer's disease in middle-aged Finnish men. Age and Ageing 46(2):245-249.
  3. Laukkanen T et al., 2018. Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study. BMC Medicine 16:219.
  4. Kunutsor SK et al., 2018. Joint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk. Annals of Medicine.
Hydra Editorial

Hydra's editorial team. We write from primary research and cite every study we rely on, with its year and journal. We quantify claims wherever the evidence allows and state plainly where it does not: where a finding rests on a small or single trial, we say so in the text rather than in a footnote.